feat: Enhance invoice file backup procedure to include JSON snapshots

- Updated the stored procedure `fds__admin_backupAndClearInvoiceFile.sql` to back up not only the invoice file but also JSON snapshots of related data (invoices, items, details, service requests) to ensure consistency and traceability.
- Modified the table structure of `fds__invoice_file_backups` to accommodate new JSON columns for storing these snapshots.
- Added an ADR (0030) document to outline the decision and rationale behind these changes, emphasizing the importance of maintaining a consistent set of data alongside the backed-up file.

Fuchs_Database/dbo/Tables/fds__invoice_file_backups.sql

@@ -3,6 +3,15 @@ CREATE TABLE [dbo].[fds__invoice_file_backups] (
     [InvoiceId]    VARCHAR (10)    NOT NULL,
     [DocumentName] VARCHAR (50)    NULL,
     [file]         VARBINARY (MAX) NOT NULL,
+    -- JSON snapshots (FOR JSON PATH) of the invoice's data rows at backup time, so the file and
+    -- the data it was rendered from stay together as one consistent set (ADR 0030).
+    -- InvoiceJson: the fds__invoices row without [file]; InvoiceItemsJson: array of
+    -- fds__invoice_items rows; InvoiceDetailsJson: the fds__invoice_details row (NULL if none);
+    -- InvoiceServiceRequestsJson: array of fds__invoice_servicerequests rows.
+    [InvoiceJson]                NVARCHAR (MAX) NULL,
+    [InvoiceItemsJson]           NVARCHAR (MAX) NULL,
+    [InvoiceDetailsJson]         NVARCHAR (MAX) NULL,
+    [InvoiceServiceRequestsJson] NVARCHAR (MAX) NULL,
     [BackedUpAt]   DATETIME        CONSTRAINT [DF_fds__invoice_file_backups_BackedUpAt] DEFAULT (getutcdate()) NOT NULL,
     [BackedUpBy]   VARCHAR (25)    NULL,
     CONSTRAINT [PK_fds__invoice_file_backups] PRIMARY KEY CLUSTERED ([uid] ASC)